In a surgical operation for the therapy of brain or spinal cord diseases, typically, a hard tubular device is used for access to an intrathecal or intraventricular lesion (e.g., ependyma, thrombus, tumor, etc) which is then perforated or removed with the aid of a subminiature manipulator. For example, cerebrospinal fluid produced in the cerebral ventricle flows in the spinal direction through very narrow tubes. When even a part of the circulation path of the cerebrospinal fluid is closed, it is accumulated in the cranial cavity or the spinal cavity, causing increased intracranial pressure, with the concomitant generation of a headache and emesis. In a severe case, a brain developmental disorder, called hydrocephalus, is generated. Representative among common surgeries for the treatment of hydrocephalus are a shunt operation and endoscopic third ventriculostomy.
The insertion of a shunt into the cerebral ventricle diverts fluid from the brain into the abdominal or thoracic cavity where it is safely absorbed into the blood stream. The shunt conduit may be provided with a valve by which the amount of the cerebrospinal fluid can be regulated depending on the cranial pressure. In former days, in order to change the pressure, the valve itself had to be replaced with a new one by re-operation. Recently, valves that can regulate the pressure ex vivo have been developed, allowing the pressure to be readily reset depending on the condition of the patient. Shunt therapy is the most common surgery for the treatment of hydrocephalus, and can be applied to both communicating and non-communicating hydrocephalus.
Endoscopic third ventriculostomy is a surgical procedure that has more recently been developed, and in which an opening is created in the floor of the third ventricle using an endoscope upon the enlargement of the ventricle in non-communicating hydrocephalus, allowing communication between the ventricle and the subarachnoid space. Endoscopic third ventriculostomy has the advantage of the natural circulation of cerebrospinal fluid without the implantation of a foreign object, such as a shunt, but is used only to treat non-communicating hydrocephalus. In addition, endoscopic third ventriculostomy requires that the ventricle has a sufficient size and the floor of the third ventricle and its surrounding blood vessels be suitably structured to perform the operation. Further, the probability of success is high only when the operation is performed on children one or more years old. It is also known that endoscopic third ventriculostomy does not work well on hydrocephalus caused by cerebral hemorrhage or central nervous system infection because the superior sagittal sinus where the cerebral spinal fluid is finally absorbed is often obstructed. Unless hydrocephalus is improved with endoscopic third ventriculostomy, an additional shunt therapy should be undertaken.